Clutch disk assemblies used in vehicles function as a clutch for engaging and disengaging a flywheel. Clutch disk assemblies also function as a damper mechanism for absorbing and damping torsional vibrations from the flywheel. In general, vehicle vibrations include idling-related noises such as rattling sounds, traveling-related noises such as rattling associated with acceleration and deceleration and muffled noises, and tip-in/tip-out (low frequency vibrations). The damper function of the clutch disk assembly is provided ideally to eliminate these noises and vibrations.
Idling-related noises are rattling noises that emit from the transmission while the gearshift is put into neutral and the clutch pedal is released, for example, while waiting at a traffic light. In the engine idling rotational speed, the engine torque is relatively low and the torque fluctuations at the time of each power stroke explosion is relatively large. Under these conditions, the teeth of the input gear and counter gear in the transmission undergo a phenomenon of striking against one another.
Tip-in and tip-out or low frequency vibrations refer to large-scale lengthwise shaking of the vehicle that occurs when the accelerator pedal is depressed or released suddenly. If the rigidity of the drive transmission system is low, the torque transmitted to the tires is transmitted back from the tires as torque and a resulting lurching reaction causes excessive torque to be generated at the tires. As a result, longitudinal vibrations occur that shake the vehicle excessively back and forth.
In the case of idling noises, since the problem lies in the zero torque region of the torsion characteristic of the clutch disk assembly, the torsional rigidity is preferably low in the region. Conversely, it is necessary for the torsion characteristic of the clutch disk assembly to be as rigid as possible to suppress the longitudinal vibrations caused by tip-in and tip-out.
In order to solve this problem, a clutch disk assembly has been proposed that has a two-stage characteristic obtained by using two types of springs. The first stage or low torsional angle region of the torsion characteristic has a relatively low torsional rigidity and low hysteresis torque, and provides a noise preventing effect during idling. Meanwhile, the second stage or high twisting angle region of the torsion characteristic has a relatively high torsional rigidity and high hysteresis torque. Thus, the second stage is sufficiently capable of damping the longitudinal vibrations of tip-in and tip-out.
A damper mechanism that efficiently absorbs small torsional vibrations has also been known. The damper mechanism is configured to have a low hysteresis torque in the second stage of the torsion characteristic and does not allow a high friction mechanism of the second stage to operate when small vibrations are inputted due to such factors as combustion fluctuations in the engine.
There has also been known a flywheel assembly that configures a torsional vibrations damping system that is divided by the input and output sides so that the damper mechanism is the border, in combination with the damper mechanism.
The flywheel assembly is made up of an input side first flywheel, an output side second flywheel, and a damper mechanism for elastically coupling the both flywheels in a rotational direction, for example. The damper mechanism includes a plurality of coil springs, and further includes a friction generating mechanism or a viscous resistance generating mechanism. A clutch cover assembly is attached in the second flywheel, and a friction coupling portion of the clutch disk assembly is disposed between a friction surface of the second flywheel and a pressing surface of a pressure plate. The clutch disk assembly is coupled to an input shaft of the transmission.
There has been known a flywheel assembly directly outputting torque to the input shaft of the transmission without the clutch cover assembly and the clutch disk assembly along the path. The flywheel assembly has a damper mechanism that is the same as that of the clutch disk assembly, and a hub is coupled to the input shaft. A flywheel is fixed to at least one of the input member and output member of the damper mechanism.